Grid structure for electron discharge device



Jan. 8, 1952 w. N. PARKER 2,581,876

GRID STRUCTURE FOR ELECTRON DISCHARGE DEVICES Original Filed March 30,1949 3 Sheets-Sheet l Zhwento:

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C(ttorneg Jan. 8, 1952 w. N. PARKER GRID STRUCTURE FOR ELECTRONDISCHARGE DEVICES 3 Sheets-Sheet 2 Original Filed March 30, 1949 311mmor WiYlz'am A/t Par/ 2r W I Gttorneg m l l nl Jan. 8, 1952 w. N. PARKER2,581,876

GRID STRUCTURE FOR ELECTRON DISCHARGE DEVICES Original Filed March 30,1949 3 Sheets-Sheet 5 INVENTOR WILLIAM N. PARKER Patented Jan. 8, 1952GRID STRUCTURE FOR ELECTRON DISCHARGE DEVICES William N. Parker,Lancaster, Pa., as signor to Radio Corporation of America, a corporationof Delaware Original application March so, 1949, Serial No.

Divided and this application November 22, 1949, Serial No. 128,783

' 8 Claims. ((31.313-348) The invention relates to a novel electrodestructure and method and apparatus for making the same, which is usefulfor making parts of the electrode structure of an electron dischargedevice, more particularly grids. However, the field of application ofthe invention is much broader and the invention may be practiced in theconstruction of various articles of manufacture.

This application is a division of my co-pending application, Serial No.84,406, filed March 30, 1949, now Patent No. 2,565,623, granted August28, 1951, which latter application is a continuation-inpart of theco-pending application of L. P. Garner" and W. N. Parker, Serial No.18,114, filed March 31, 1948. In the said application of L. P. Garner.and W. N. Parker there is fully disclosed and claimed the method forreducing the wall thickness of tubing or flat sheets in the ratio ofapproximately 30 to 1 in one pass of the work through the apparatus andforming walls of foillike thickness.

The process for reducing the wall thickness of the tubing is animportant feature of the invention in that the means for reducing thewall thickness embodies a basic mechanical process including steps offabricating the shapes which are substantially the end product withoutthe use of additional apparatus, said products being characterized byinherent novel features not heretofore embodied in given specificstructures of eprior art.

Although the invention in its various aspects has wide application, forpurposes of illustration,

it will be; described particularly in connection with the manufacture ofgrid electrodes for electron discharge devices. From this disclosure, itwill be,- -a ppreciated that the invention involves t. nly an apparatusbut also a method of opering the apparatus which constitutes a process fpf forming the resulting article. Furthermore, the formed articles perse embody novel features which are improvements over similar articlesheretofore produced and used in tube construction.

In electron tubes having one or more grid electrodes it has been theusual practice to form each grid from separate parts as by welding,binding or swaging, into a desired cylinder or other shape. Theoperation is tedious and the resulting parts lack the mechanicalaccuracy required for closely spaced electrodes in tubes capable of highperformance. The close mechanical tolerances desirable inmulti-electrode discharge devices are difllcult to maintain due to theinherent lack of ricated which embody constructional features I 2rigidity of such electrode assemblies. Even though great care is used tomake the spacing substantially uniform when the tube parts areassembled, the non-uniform stresses induced by the spot weldingoperation customarily employed heretofore in the manufacture of grids,induces well known disadvantageous features; for example one detrimentalfeature may be serious deformations occasioned by the use of heat in theexhaust process for driving out gas in the electrode structure. Thejoints between the multiplicity of wires and similarparts do not conductheat as well as solid metal, which is a source of undesirable tubecharacteristics.

Electron tubes used to generate appreciable amounts of high frequencypower are usually operated so that the grid electrode is positive withrespect to cathode during a part of the alternating current cycle, withthe result that the grid is bombarded by electrons and is consequentlyheated. Unless this heat is :eadily dissipated by radiation and/or endconduction, the grid wires may become sufliciently hot as to emitelectrons, and inefficient and improper tube operation may result.Inadequate grid dissipation frequently seriously limits the outputcapability of high power tubes. On the other hand, when such tubes areoperated at high radio frequencies, the electrodes must carryconsiderable current required by the inter-electrode capacities. Thiscurrent may also cause objectionable heating of the grids unless thegrid paths are of low electrical resistance to the high frequencycurrents. Conventional spot welded grids have high resistance junctionsat the welds and the materials used usually have high electricalresistance.

The present invention eliminates or largely overcomes the abovementioned difliculties, as well'as others, in that the source of thesedifliculties are removed by a novel construction which results fromcarrying out my novel process so as to produce an improved end productfree from structural defects which are responsible for producing theaforesaid deleterious eliects currently inherent in electrode structuresand/or assembl es.

Thus a principal object of my invention is to provide a process wherebya grid electrode may be fabricated from a unitary piece of workmaterial.

Another object is the provision of a process whereby novel gridstructures may readily be fabfar superior to those heretofore attainableand yet may be readily fabricated at a reduced cost.

' quency currents.

Another object of the invention 151m provide thermal resistance,continu- Figure 9 is a side elevation of a still further modification ofa completed grid;

Figure 10 is a section partly schematic of a modified form of apparatusutilized in forming a planar grid;

Figure 11 is an elevational view, partly in section of'the etchingstep;.

Figure 12 is an elevational view of a mandrel constructed in accordancewith my invention,

'being a modification of the mandrel shown in Figure 1; and v Figure 13is an elevational view of a grid electrode embodying the invention.being a further modification of the electrode shown in work part such astubing which is an integral piece and may be fabricated into a unitarystructure, as for example the combination of a grid and its supportingmember.

Another object is the provision of an improved electrode structurecharacterized by having several component parts integrally connected,thus avoiding any welding or equivalent operation in joining the variousparts together, as for instance in the making of grids.

Another object of the invention is to provide an improved method ofmaking wire electrodes for electron discharge devices which may berigidly secured at each end yet will not bow or buckle when heated andwhich are easy to install.

A special object of the invention is the provision of a process for,making an electrode by greatly reducing the wall thickness of the stockmaterial, such as tubing, processing portions of the tubing intocavities of a tool, which leaves a web of extreme foil-like thinnessbetween said processed portions, and subsequently removing the partlyformed work from the ap paratus in such a condition that the webportions may be removed in any suitable manner.

Other objects, advantages and results of the invention will manifestthemselves from a reading of the following description in connectionwith the accompanying drawings.

Various applications of the invention are shown in the accompanyingdrawings in which: Figure 1 is an elevation, partly in section, of

one form of apparatus for performing the invention;

Figure 2 is a section taken on the line 2-2 of Figure 1;

Figure 3 is an enlarged cross section taken through the axis of themandrel and metal cup, showing the wall thinning operation;

Figure 4 is an end cross section, along the line H of Figure 5, of themandrel and tubing,

' showing the metal forming thegrid wires pressed site sides thereof;

Figure 8 is an elevation partly in section of the mandrel constructionfor making the type of gridshowninFigure "I;

Fi ure 6.

According to my present invention, I place a blank upon a suitable hardbacking surface having a plurality of grooves formed therein. Inaccordance with the process described and claimed in the above-mentionedco-pending application of L. P. Garner and W. N. Parker, Serial Number18,114, filed March 31, 1948, I effect a tremendous reduction in thewall thickness of the blank by transmitting the necessary forces throughthe portion of the blank to be worked rather than through the workedportion. As the wall thickness is being reduced the material of theblank is simultaneously forced into the grooves of the backing surfaceleaving a web portion interconnecting all of the relatively thickerportions which extend into the grooves. The interconnecting web portionis of foil-like thinness and has a cross section thickness of the orderof .0004 inch which may readily be removed, as will be pointed outhereinbelow, leaving fine wires which are integral with common endpieces at each end.

Referring to the drawings, more particularl Figures 1 to 3, apparatusfor practicing my inventionin forming a grid having a cylindrical arrayof .wires maycomprise a machine tool similar to a drill press. Sincethese tools are well known, only the parts essential to an understandingof the invention are shown. A rotating shaft 32 is movable up and downby operation of a handle 2 which slides a sleeve 3 by means of a gear 8.A mandrel 5, having a plurality of slots 50, has closely fittingbearings ill in a yoke 6 which isin turn attached to a base 1.. .The-

roller 3 mounted in a slide block l4 slidable' within frame 9. I I

In Figure 3 is most clearly seen a work part or blank I in the processof having 'its'wall thinned by the apparatus of Figures 1 and 2. Thework part or blank I has a part I I which has been thinned, thethickness of'which has been shown exaggerated for purposes ofillustration and actually is extremely thin, has yet thinner portionsand of the order of a few 10,000ths of .an inch as pointed outhereinabove, which forms the interconnecting web between the relativelythicker portions which extend into grooves 5a of the mandrel. The wallthickness of the metal tube l is reduced by the simultaneous applicationof axial pressure in the direction, of arrow l8 (Pig. 3) and radialpressure in the direction of -volume of material. -the worked portionwill be extended in propor- "arrows'2ll exerted while the tube is underthe rollers. The mandrel serves to back up the inner surfaces of thetube in the region opposite the rollers, and to transmit the necessaryrota- :tional torque 2i to the work part through clamping devices whichmay'comprise a collar-22 provided with a set screw 23 (Fig. 3), or acollar 28 provided with teeth 21. The relatively small radius bead 15 onrollers ll, l2 and I3 provides intense local pressure in region 24 ofthe tube section II, causing plastic deformation and consequent thinningdown of the thickwall of the tube. The worked portion flows out underthe rollers and along the mandrel away from the portion to be workedwith substantially no loss in As a result the length of tiallycorresponding to the dimensions of wires- 30 (Fig. 6) of the grid to beformed. As an example there may be- 60 exactly spaced grooves 5a, each.006 inch wide by .006 inch deep. These grooves may be ground in thehardened steel mandrel and any convenient expedient used to indicate thedepth of the grooves during grinding. Universal coupling 3| (Fig. 1)conveys to the mandrel 5 both the rotary motion of the shaft 32 and theaxial motion of sleeve 3 without vibration or eccentricity so thatmandrel 5 runs true with respect to the rollers. Any other suitablearrangement may be used. The rollers ll, l2

and I3 are preferably made of hardened steel carefully formed andpolished. The hardness of the rollers should measure about 64 Rockwell Cit is possible to effect tremendous reductions in.

the work by a single pass of the same through the reducing device. Dueto the elongation of the work piece th free or lower end thereof asviewed in the draw-. ings projects over the lower end of the mandrelafter the reducing process is started. .In view of the extreme wallthinness of the worked portion it is necessary to provide some means forovercoming the substantial vacuum which obtains inside the work piecewhich extends below the end of the mandrel when the work blank has aclosed end as in Figure 3. To overcome this I either provide a small airpassage Tl in mandrel 5 or an air passage or hole 18 in the work piece(Fig. 5).

The partly completed grid shown particularly in Figure 5, upon removalfrom the mandrelis' ready for further processing to remove web portionsI'm from between the thicker portions of the work. The work is firstthoroughly degreased work first in a bath of a 50 percent solution ofwhilethe hardness of the mandrel should measure between 64 to 66Rockwell C.

With the work piece I, mandrel 5 and associated parts 28, 3| and 32 allrotating at a speed of about 700 revolutions per minute, feed screw 33is advanced by means of knurled handle 34. This causes slide H to movetoward work piece I and force rollers ll, l2 and I3 thereinto apredetermined depth as set by nut 35 and locknut 36. This depth is sochosen as to bring heads I 5 towithin a few l0,000ths of an inch of themandrel so as to givethe desired extremely thin inter- /connectingweb/lla between grooves 5a and to facilitate tlie flow of metal into thedepressions formed in the mandrel. Handle 2 is now operated so that theattached gear 4 and associated rack 31 of the drill press exert adownward axial force I! on work piece I; simultaneously thefricco-pending application and I do not believe it is necessary torepeat the same here. However, it should be understood that in thepresent process and as pointed out in said co-pending application thenecessary forces to form the work are transmitted to the work piecethrough the portion to be worked; thus once the worked portion has beenreduced and forced out from under the rollers it is substantially freeof any forces.

Since the worked portion is not called upon to nitric acid in distilledwater. This rough etch-is carried to the point where the webbing firststarts to disappear or when holes first start to appear therein. Thenthe final etching is carried out in a 30 per cent solution of nitricacid in distilled water. Here the etching proceeds at a considerablyslower rate due to the lower concentration of the acid, permittingcontrol over the grid wire size which determines the correct time tostop the etching. During the etching the bath is constantly agitated. Asthe etching proceeds, there will first be large ragged pieces of thewebbing left on the grid wire edges. Gradually these ragged piecesbecome smaller and disappear leaving the edges of the grid wires smooth.As soon as this occurs the work should be removed from the etching bath,rinsed in a bath of chromic acid (CIOs) after which it is further rinsedin running water fora suflicient length of time to remove a wide varietyof tubular or planar parts or com-' binations of various diametersand/or wall thicknesses. Further, the process is applicable to prac-'tically all ductile, materials from relatively soft copper as in thecase of work piece I and alumiother than copper are utilized, theetching bath concentrations vary accordingly. For example, I have founda suitable-etching bath for tantalum to be hot hydrofluric acid with atrace or small quantity of nitric acid.

It should be further understood that the shape of the work blank beforeprocessing is not limited to having a cupped or closed end l6 (Fig. 3)but may be tubular with both ends open (Fig. 1) or the lower end may beprovided with a perforated shield by a prior operation. The interiordiameter of the work blank need not be uniform throughout. portionsother than that processed to form the grid wires may be of differentshape or diam- 7 eter. Furthermore, the outside diameter may, be variedas desired as the work is passing through the reducing device by merelyadjusting handle NandnutsflJB. f i. V Grids of various dime ons andgeometry may be made by practicing the present process: For example wehave made grid electrodes .420 inch in diameter for ninety wires .003inch thick as well as grids .850 inch in diameter for ninety .007 inchdiameter wires, with variations in lengths including six inches,Furthermore. the longitudinal wires of the grid need not be of uniformwidth. They may be wide at one end and narrow at the other withreversely tapered slots therebetweemsuch as the electrode of a singlepotentialimage tube disclosed in the application of Gardner L. Kriegerand George A. Morton. filed June 28, 1946, Serial Number 679.928nowPatent No. 2,572,494, granted October 23,-195l,.- relating toVelocity Selection In Electron Tubes. Such a' form of grid is shownherein in Figure 9, more fully referred to hereinafter.

With a properly shaped backing surface or mandrel the grid may bereadily formed with' an integral support of foil-like thinness.

By using a mandrel with spiral grooves a.v grid with spiral wires may beformed. In Figure 7 there is shown an electrode structure produced bythis process which has two sections of reversely spiraled wires 62Joined at the center by band "68 which may have the same radialthickness as the wires. This structure automatically accommodatesthermal expansion of the wires 62 by rotation of the middle band 63 eventhoughthe thicker ends 64 are rigidly anchored. Such an electrodestructure is useful as a directly heated cathode or as a grid in anelectron tube as described by Lloyd P. Garner in United States PatentNo. 2,165,135. However, the manufacture of such a structure is greatlysimplified by the use of the process which is included in the subject ofthe present invention. The mandrel in the present case is free to movewith respect to the work and is made in two parts'separable at thecenter groove which forms mid-band 68 so as to allow removal of theformed part.

The procedure for forming the zig-zag grid illustrated in Figure 7 maybe explained with reference to Figure 8, which latter shows such a gridin the process of being formed. The mandrel consists of lower part 66which is removable from center part 66 by loosening nut 61. Center part68 is free to slide and turn with respect to upper part 68 by means ofextension 68. Upper part 68 supplies the axial thrust and driving torquetowork blank by means of teeth 21.

Grooves 1| are reversely complementary to grooves 12.

Withmetal work blank 10 revolving,- rollers ll. 12 and are fed inradially as before near end 64 which causes metal to enter grooves N.Then as an axial force is exerted, in the manner heretofore explained,spiral wires 62 will form in grooves II with a thin web between them. Asthe forming process progresses over the junction of parts 65 and 66,metal flows into the peripheral groove forming mid-band 63. From thispoint on the keying action of mid-band 63 prevents relative movementbetween end 84 and parts 66 and 66 so that further lengthening of workblank 10 requires a separation or moving out of parts 66, 66 and 68relative to part 68 and work blank 10. When the required length offorming has been attained the rollers are backed oif and the assemblycomprising parts 66. 66 and 61* and 70 direction of the leadin wires.

"accuses 8 the formed 62. 68. ll comprising he completed work part IIIare removed from upper part 68. Nut 61 is then removedandpa'rts '86 and-68 unscrewed along spiral groo'ves'll and 12- respectively, in thesequence indicated, leaving the substantially completed work part readyfor completion by removing the foil-like webs be tweenthewirlasfl. 1 H

Ffom the foregoing description it will be 'ob 1o vious to workers in theart that various modifications of the invention will suggest themselvesand it is my intention to cover all such modiflca tions as coine withinthe scope of the appendedclaims. For example the longitudinal wires of 5the'grid need not be' of uniform width as previously pointed out. Asillustrated in Figure 9 the wires may take the form of slats "18' whicharewide at one end and narrow at the other, and the webs l6thereb'etween are re'versely go tapered. The ends of the slats 14terminate in thicker end ferrules I6.

It should also be appreciated that the form of backing surface ormandrel may be other than cylindrical. The apparatus illustrated inFigure 10 is suitable for forming a blank or work-piece 88 of sheetmaterial such thatafter removal of the web portion it will yield aplanar grid-'or'the like. The apparatus may'comprise a car pro-- videdwith rollers 8| whichrun in groove 82. The

groove 82 i's'formed in a constraining member 84. Inthe arrangementshown, a reciprocatory motion may be provided by the crank 86' and connecting rod 81, which is the equivalent of the rotational motion of theprevious example. The

5 force 88 is at right angles to the principal motion,

and may be applied by any external means (not shown). Suitablemeans'which may be ofa conventional form, would be required to maintainsdesired limit of separation betweenthe backing m member 85 and theroller ii. The scanning pattern generated by the rapidreciprocatingmotion will be zig-zag. and the pitch thereof need not beconstant across the width of the scanned area,- i. e., it may be coarse,followed by arelatively fine pitch so as to-produce a variablepitchscanning pattern. In any event, the scanning cycles should overlap toproduce the proper'scanning effect, and the tension stresses as inconnection with the other modifications described herein; should bewithin the elastic limit of theportions b0 undergoing extrusion.

As in the case of mandreli, backing member 86 is provided with grooves85a. After removal of the work 88 it maybe further processed by etchingas pointed out hereinabove in connection as with work piece I.

Referring to Figure 4; it is alsoobvious that the. purpose ofreinforcing or imparting added rigidity to the grid wires 38,'a selectedorder or arrangement may-involve making some of the wires substantiallylargerin cross section than the rest. This may be accomplished by makingevery third orfourth groove 29 of the mandrel 6. deeper, and thuspermitting more of the metal of the work piece I to flow into thesedeeper o5 grooves. This is possible because the grid .wires or membersalways conform to the contour. of the mandrel. Besides reinforcing thegrid structure, the larger wires would correspondingly imis oftherollers II. and llneed not be constant during the longitudinal motionbut may vary in predetermined steps and/ or rates during practicing theprocess. The process, as indicated above, is applicable to practicallyall ductile materials from the relatively soft aluminum or copper toharder materials such as steel, iron-nickel-cobalt alloys, molybdenumand tungsten.

While the process as described utilizes round tubular sections over asmooth round mandrel and with external rollers, it is to be understoodthat this invention includes the adaptation where the One or morerollers are on the inside of the tubular work piece and the backingsurface consists of the inside wall of a hard cylinder.

As pointed out hereinabove, a grid may be readily formed in accordancewith my invention with an integral support. A mandrel 90 is shown inFigure 12 which is suitable for forming such a grid and integral support9| (Figure 13). As shown, the upper portion 92 has grooves formedtherein and has a smaller outside diameter than the lower portion 93.Between the lower portion 93 and upper portion 92 lies shoulder 94. Thewires 95 and integral support 9'3 are formed in accordance with theprocess set forth hereinabove with respect to work piece I except thatas rollers II, I! and I3 approach shoulder 94 they are backed offsomewhat to clear the lower portion. The worked surface of support 96affords a highly accurate locating or jigging surface which facilitatesaccurate positioning of the electrode.

I have also removed the foil-like web "a by means of a turning toolmounted in a lathe. However, at the present time I prefer to remove theweb by means of etching.

Various other modifications of the invention may be made in itsapplication to various types of devices but the ones described and/orsuggested may be regarded as illustrative of the scope of the inventionwhich is only limited by the prior art and appended claims.

Iclaim:

1. A one piece electrode comprising a pair of end portions, one at eachend of said electrode, and an array of elongated wires intermediate saidend portions and integral therewith, said wires having a cross-sectionalthickness of from .003 to .907 inches and being substantially thinnerthan said end portions.

electrode comprising a one piece body having end portions one of whichis of a predetermined thickness and a plurality of strands intermediatesaid portions and integral therewith, said strands being substantiallythinner than said portion and having a cross-sectional thickness of from.003 to .007 inch.

3. An electrode comprising a seamless one piece elongated tubular bodyhaving end portions of a predetermined thickness and a cylindric arrayof spaced apart strands intermediate said portions and integraltherewith, said strands being substantially thinner than said endportions.

4. A grid electrode for a high frequency electron discharge device,comprising a seamless one piece elongated tubular body having endportions of a predetermined thickness and a cylindric array of closelyspaced filamentary strands intermediate said portions and integraltherewith, said strands being substantially thinner than said endportions.

5. A one-piece grid electrode for an electron discharge device,comprising two end portions, and an array of elongated wires integralwith said end portions, said wires having a crosssectional thickness offrom .003 to .007 inches and being substantially thinner than at leastone of said end portions.

6. A one-piece grid electrode for an electron discharge devicecomprising a seamless tubular support member, a cylindric array ofelongated wires individually extending from said support member andintegrally joined therewith on their one ends, said wires having across-sectional thickness substantially less than that of said supportmember, and an end portion of the same order of thickness as said wiresand of circular perimeter on which said wire individually terminate andto which they are integrally joined on their other ends.

WILLIAM N. PARKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,654,471 Schrack Dec. 27, 19272,264,735 Baker et al. Dec. 2, 1941 2,414,785 Harrison et al. Jan. 21,1947

